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Steam Reforming : C1 Vs. Lpg (C3 And C4)

hydrogen reforming

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#1 H2_Song

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Posted 19 September 2019 - 01:38 AM

Dear all,

 

 Recently, Hydrogen has become a very promising candidate for the new energy carrier and my company has been looking for a fit and economic H2 production method to the local market. The local market has well-established supply network for natural gas and LPG, so these are main feedstock for H2 production. Myself and the company are very familiar with steam methane reforming technology and its details as we operate several units on our own; however, we know little about LPG(C3 and C4) reforming. 

 

In this regard, I would like to ask the forum to kindly provide general difference between C1 and LPG reformer, and what changes can we expect within the system from C1 to LPG. I have given a thought about changes and they can be the followings. Please correct me if wrong.

 

  1. Desulfurizer : LPG general contains more sulfur contents, so need more catalysts and adsorbents for HDS and ZnO?

  2. SR Reactor : For the same amount of H2 production, less LPG molar flow is needed. Reactor size may be reduced? 

                            Do we expect the same GHSV for both C1 and LPG steam reforming reaction?

  3. WGS : As CO contents at the downstream of SR reactor would be higher than that of C1, size of WGS reactor may increase?

  4. PSA : Just like the reason addressed on item 3, size of PSA may increase?

 

I may have not addressed enough, so I would like to kindly request the forum to share your thoughts on this topic.

 

Kind regards,



#2 PingPong

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Posted 19 September 2019 - 06:21 AM

.... we operate several units on our own; however, we know little about LPG(C3 and C4) reforming.
Is it the intention of your company to convert one or more of the existing units from natural gas to LPG feedstock ?

#3 H2_Song

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Posted 19 September 2019 - 08:06 PM

We have not decided anything at the moment, and it is a business decision we cannot make until we know changes and difference between C1 and LPG steam reformer. We are certainly considering a retrofit to the existing ones, but it really depends on the magnitudes of changes (costs).

 

Thank you for your time to go through my post!



#4 PingPong

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Posted 20 September 2019 - 07:49 AM

The magnitude of changes will also depend on the present design of the existing units.

Their age and which licensor designed them will have an impact on the necessary changes, or on the resulting hydrogen production capacity if only the minimum required changes for LPG are implemented.

 

The XOT and COT for which the reformer furnace has been designed, as well as the design S/C ratio,  have an impact on the required changes to achieve present hydrogen production capacity, or on the maximum hydrogen capacity without excessive changes to the unit.

 

Some of the existing units may not be suitable for an economical retrofit to LPG feedstock.

 

In addition to the impact on HDS, ZnO, WGS and PSA there are more changes required:

 

First of all new equipment is required to vaporize the LPG. That takes energy, which can be taken from steam condensation, or from heat integration with the syngas effluent cooling in the unit.

 

A prereformer vessel is likely required, which will also require some changes to the convection bank of the furnace.

Without a prereformer the XOT and COT may have to be lowered and the S/C ratio further increased.

 

The reformer furnace fired duty may increase.

 

Reformer furnace burners may be impacted due to more PSA tailgas to be burned.

 

Syngas effluent cooling train may need modifications due to more duty to be removed, in addition to changes to vaporize the LPG feed.

 

 

It takes a detailed study by a reputable licensor to determine all required modifications for each of your units.

 

But before you initiate such study you should check whether LPG feedstock in your country is going to be sufficiently cheaper than natural gas (on a $/MJ or $/MMBTU basis) for many years to come to justify the cost of all required unit modifications.

Frankly I have a problem believing that.



#5 H2_Song

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Posted 22 September 2019 - 08:51 PM

Dear Pingpong,

 

These are excellent discussion points. Major portions of your points are well understood.

 

Just one thing I would like to know is that the existence of pre-reforming would actually help the reaction. I have gone through some literature related to C3 and C4 reforming, but it seems that just a sole reactor seems sufficient for complete reaction considering GHSV and reaction rate.

 

I understand that you brought the point because you assumed we would use the existing reactor, so pre-reformer is required to compensate? or Do we need pre-reformer for C3/C4 reforming even if we start from the scratch?

 

Thank you for your kind reply in advance.

 

(p.s. we have a reliable LPG supply with competitive price for long term period, just for your information.)



#6 PingPong

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Posted 23 September 2019 - 02:45 AM

A prereformer converts the C3/C4 feed into a mixture of C1, CO, CO2 and H2, so it not only does some conversion but also assures that no C3 and heavier components enter the radiant coil.

 

Without a prereformer C3 and C4 will enter the radiant coil as such and therefor the XOT will need to be lower than with a prereformer, or in the present operation with natural gas feed, so as to minimise carbon deposits. Also the COT may have to be lowered and/or S/C ratio may need to be increased for same reason.

 

What needs to be done depends on the actual design of each existing SMR, what future hydrogen production capacity you want from the existing units (the same, or lower, or maybe even higher), and what run length you want.

 

I will also depend on the licensor that you involve to do the retrofit design for LPG feed. One licensor may include a prereformer, resulting in a more efficient design (more H2 per ton of LPG and fuel), while another may not.

 

In general: revamping an existing unit always requires more changes than one thinks before the redesign starts.

And not only ISBL but also OSBL and utility systems.

 

In your case you also need to think about storage of the LPG feed. Will a feed surge drum be sufficient, or will storage sphere(s) be needed? That depends on the reliability of the LPG supply.

 

Another point to think about: does the revamped unit still have to be able to operate on natural gas feed only? That will affect the way the LPG feed is best vaporized.


Edited by PingPong, 23 September 2019 - 02:47 AM.





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